Hot deformation of cast AZ31 and AZ80 magnesium alloys – Influence of Al content on microstructure and texture development

Abstract

The present research studies and compares the hot deformation behaviour of the AZ31 and AZ80 magnesium alloys. Uniaxial compression tests using a Gleeble® 3500 thermal-mechanical simulation testing system were conducted at 400 °C and constant true strain rates in the range of 0.001 s−1 to 0.1 s−1. Samples were deformed to various levels of strain to assess the progression of dynamic recrystallization. Detailed microstructure and texture characterization were performed using optical microscopy, XRD macrotexture measurements, and electron backscatter diffraction (EBSD) microtexture measurements. Both the starting materials showed coarse dendritic microstructures and random texture. Both discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) occurred in both the alloys during deformation, although the AZ31 alloy showed a higher tendency towards CDRX compared to the AZ80 alloy, while reverse was true for DDRX. The AZ80 alloy showed initiation of DDRX at lower deformation strain levels, had coarser DDRX grain size and a higher DDRX% compared to the AZ31 alloy. These features resulted in the development of a homogeneous fine-grained microstructure in the AZ80 alloy for deformation to an equivalent strain of 1.0, while the microstructure of the AZ31 alloy sample became bimodal. The choice of the alloy also affected the texture development during the deformation, with the AZ31 alloy showing DDRX texture randomization, while the AZ80 alloy showing deformation texture preservation by the DDRXed grains. The study highlights the substantial effect the Al content in the α-Mg solid solution has on the microstructure and texture development during hot deformation of the AZ alloys.